Example embodiments of the present invention disclosed herein relate to flash memories. For example, an example embodiment of the present invention relates to a flash memory device capable of adjusting a pass voltage level and a programming method thereof.
Recently, as flash memory devices have decreased in size, interest in assuring pass voltage windows has increased.
In practice, during a programming operation of a flash memory device, a program voltage is applied to a selected word line while a pass voltage is applied to unselected word lines.
Program voltage disturbance caused by a low pass voltage results in a malfunction to program-inhibited memory cells from among a plurality of memory cells coupled to a word line to which the program voltage is applied, resulting in a failed programming operation. On the other hand, pass voltage disturbance caused by a high pass voltage results in a malfunction to memory cells among the plurality of memory cells coupled to the same cell string, to which the pass voltage is applied, resulting in a failed programming operation.
Thus, the pass voltage window defines a range of the pass voltage that does not result in the pass voltage disturbance and the program voltage disturbance. A broader pass voltage window increases a reliability of the flash memory device.
However, in practice, a pass voltage window is only determined after fabricating out a wafer including flash memory devices. If there is an insufficient pass voltage window, a programming method must be modified and revised several times, which delays a development or turnaround time of the flash memory devices.